I realize that this is in a different venue than his original statements, but it nonetheless seems potentially relevant to figuring out what Kennedy meant in his original comments:

McCain, who was a prisoner of war in Vietnam, said Iraq was different from Vietnam because there "is desire on the part of the people of Iraq to have their own democratic government . . . and we have the capability militarily and politically to prevail and we did not in Vietnam."

But Democratic Sen Edward Kennedy of Massachusetts said, "Vietnam ended up in a quagmire. Iraq is as well."

As reader Tom Westberg, who pointed this out to me, observes, "Quagmire is not about deception. It's about losing." And this suggests that Kennedy's earlier "Iraq is Bush's Vietnam" remarks, though made in the context of a discussion of alleged deception, were about losing as well.